It is often necessary or desirable to infuse a flowable material or fluid, which may be a liquid, a gas or a combination thereof, into the vascular system of a patient. One example is the administration of parenteral fluids to a patient.
A typical infusion system includes an infusion device for delivering the fluid and conduit means for conducting the fluid from the infusion device to the patient. The conduit means typically comprises flexible tubing leading from the infusion device to the patient and a cannula, such as a needle or catheter, for insertion into the vascular system of the patient. In normal operation, the infusion device delivers the fluid through the tubing and the needle to the vascular system of the patient.
One problem with infusion systems of this type is a condition known as infiltration. Infiltration is a condition in which infused fluid finds its way into extravascular tissues rather than simply being released into the blood stream. Such a situation occurs when the needle is not in communication with the interior of the vessel into which the fluid is to be infused. When this occurs, fluid is infused into the interstitial spaces between layers of tissues. Thus, the patient is deprived of proper intravenous drug administration and is further subjected to possible toxic or caustic effects associated with infused fluids being in direct contact with body tissues.
Infiltration is not the only possible type of anomaly associated with intravenous therapy which can cause the fluid to be improperly supplied to the patient. Other conditions which can cause abnormal infusion include venous inflammation and swelling at the infusion site (phlebitis), clotting, and a wide variety of obstructions of the conduit means, such as kinking of the tubing which supplies the fluid to the patient. Many of these affect fluid flow characteristics in a manner similar to infiltration and can, therefore, be detected by infiltration detection devices.
The goal of an infiltration detection system is to identify an abnormal infusion as early as possible without generating an excessive number of false alarms. Early detection allows the attending medical staff to rectify the problem before significant tissue damage has been done by the infiltration and before the patient has been deprived of a significant amount of the intravenous therapy. On the other hand, if the detection system is too sensitive, false alarms will result. This is very undesirable since, from a clinical perspective, establishing a new intravenous site can be difficult and time consuming. During the time necessary to start the new IV, which can be hours in some cases, the patient is not receiving the desired treatment.
Bobo U.S. Pat. No. 4,648,869 discloses a significant advance in the field of infiltration detection systems and methods. According to the Bobo patent, an infusion system infuses a test pulse or rate pulse of fluid to a patient. The test pulse creates a pressure wave response in the conduit which can be monitored and used to detect whether abnormal infusion has occurred.
Butterfield U.S. Pat. No. 4,710,163 discloses an infusion system which uses the test pulse-pressure wave response concept of the Bobo patent. However, the Butterfield system compares the test pulse pressure wave response with a reference pressure wave response which represents the normal response when there is no infiltration. Specifically, the area between the two curves representing these responses is used to attempt to detect infiltration. Thus, the Butterfield approach has the disadvantage of requiring that a normal pressure wave response be first determined and then stored for later comparison.
Bobo et al. copending Pat. application, Ser. No. 165,619, entitled Automatic Infiltration Detection System and Method, filed Mar. 8, 1988, utilizes the test pulse-pressure wave response concept of the Bobo '869 patent, but to determine whether abnormal infusion is occurring, Bobo utilizes the area between a baseline and at least a portion of a pressure versus time curve which represents the test pulse pressure wave response. With this technique, it is not necessary to first establish a normal pressure wave response for a patient, nor is it necessary to compare the assumed normal response to the test pulse pressure wave response. Rather, all that is required to make accurate determinations as to the proper supply of fluid to a patient is appropriate area information from the test pulse pressure wave response.
All of the infiltration detection systems known in the art and those described in the Bobo patent and copending patent application, involve a monitoring or detection system incorporated into some type of infusion control device, such as a pump or controller. The infusion device is then programmed or controlled to deliver a test pulse and to monitor the pressure-wave response in the conduit line to the patient, as well as supply the fluid to the patient in the normal or selected delivery pattern.
There is a need for an infiltration detection system that is independent of the infusion device and that can be used with any manufacturer's IV control device, as well as a gravity controlled infusion system, and eliminates the need for hospitals to replace existing infusion pumps with new infusion pumps capable of detecting infiltration.
It is therefore an object of the present invention to provide a stand-alone, in-line infiltration detection device that is small, lightweight, and capable of implementing the rate pulse technology without the complexities and expense of an infusion pump or device.
It is another object of the present invention to provide a stand-alone, in-line infiltration detection system that is compatible with any manufacturer's infusion pump or device, as well as gravity controlled infusion systems.
It is another object of the present invention to eliminate the problems associated with height differences between the pressure transducer and the patient's IV site, by providing a stand-alone, in-line infiltration detection device that may be placed in close proximity to the IV site.
It is a further object of the present invention to provide a stand-alone, in-line infiltration detection system that delivers a test pulse without the noise caused by background flow in an infusion pump, thereby providing a quieter environment for the test pulse stimulus, resulting in less noise and therefore improved signal discrimination.